The invention is directed to an apparatus, particularly a printer or copier, having a first electrographic printing unit that prints an image pattern onto a sheet-shaped material, having an input section via which the sheet-shaped material can be individually supplied in succession, and having an output section via which the printed, sheet-shaped material is individually successively output.
In a known high-performance printer having only a single printing unit, the individual printer components are exactly matched to one another, so that an extremely dependable operating condition with high printing performance is achieved. In order to increase the printing performance even farther, design changes must be undertaken at these components, this leading to a high development expense and increasing the probability of failure due to the redesign of the individual components.
U.S. Pat. No. 5,208,640 discloses a printer that comprises two identical printing units to which sheets to be printed can be supplied individually in succession via a common input section.
Given a printer disclosed by DE 38 18 982 C2, pairs of transport rollers are arranged in the transport path of the paper. Various pairs of transport rollers are thereby driven in common via synchronous belts by a single drive or a few central drives.
When the transport of the sheet-shaped material makes it necessary that pairs of transport rollers have different speeds or must change their rotational sense, then the rollers of the pairs of transport rollers in the previous solutions have been driven via switchable couplings. Further, gearings were arranged preceeding the transport rollers in order to set the speed and the rotational sense according to the required operating mode. Switchable couplings must also be arranged preceding these gearings. It has now been shown that such switchable couplings have great tolerances in the switching times and that high accelerations result when these couplings are switched. A further disadvantage is that the drive belts for the synchronous drive of the transport rollers are extremely long in part. The known solution is therefore very involved and has low operating dependability.